<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <ul id="target">
    <li>1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
  </ul>
  <script>
    var ul = document.getElementById("target");
    var lists = ul.getElementsByTagName("li");
    var len = lists.length;
    let frag = document.createDocumentFragment() // 创建虚拟节点
    console.log(frag);
    while (len--) {
      frag.appendChild(lists[len])
    };
    ul.appendChild(frag)
  </script>
</body>

</html>